The invention relates to a disc brake to be opened by torque arranged between a drive shaft and a driven shaft and comprising a brake wheel arrangement arranged between the drive shaft and the driven shaft, a friction surface arrangement arranged to co-operate with the brake wheel arrangement, at least one spring device arranged to press the brake wheel arrangement and the friction surface arrangement axially against each other, and cam means arranged between the drive shaft and the brake wheel arrangement, the cam means causing by the impact of the torque or rotation of the drive shaft and the possible countertorque of the driven shaft the relative axial position between the brake wheel arrangement and the friction surface arrangement to change in order to detach at least partly the braking engagement against the spring force caused by the spring device.
A known disc brake to be opened by torque is described, for instance, in DE patent publication 197 26 656. Here, the brake is opened using a complicated mechanical arrangement. Also in other corresponding structures the implementations are mechanically difficult and at the same time problematic, and therefore the most conventional way to engage and disengage the brake has been to use electromagnetic actuators.
The type of brake described above is disclosed in FI patent application 992194. Here, the drive shaft and the driven shaft are interconnected so as to be able to rotate a restricted rotational angle in relation to each other, and the means for causing the axial displacements and for detaching the braking engagement comprise cam means arranged between the brake wheel arrangement and the driven shaft. In comparison with electromagnetic brakes, an advantage of the brake of the invention primarily consists in that losses generally experienced as a drawback, such as frictional couplings of a driven device (for example the resistance to motion of a carriage to be transferred in connection with transfer gear), are utilized for opening the brake. Always when the driven device includes a sufficient amount of countertorque, the brake may open. The brake always opens, because, when the actuator (such as a squirrel-cage induction motor) is started, it has to overcome the brake torque that it experiences as countertorque. As no separate magnet is required for the brake to operate, the brake voltage in electromotor applications need not be arranged in accordance with the motor voltage, which is a considerably advantage. No rectifier is either required. The opening force of the brake does not depend on the wear of the friction surface, wherefore the brake does not have to be adjusted. The wear margin of the brake depends on the geometry of the cam elements.
Another device, especially a squirrel-cage induction motor, utilizing the cam surface arrangements is disclosed in DE patent publication 40 08 757, in which the presented structure is, however, extremely complicated and includes a large number of parts. However, here the disconnection and connection of the device is electrically controlled using microswitches, wherefore a mechanically operating solution is not concerned.
It is an object of the present invention, however, to improve the solution known from FI patent application 992194 described above so that the torques arriving particularly from the direction of the load could be managed more adequately than before without causing any safety risks. Also the acceleration of the motor caused by the pendulous motion of the load above the synchronized speed should be avoided. It is also desirable that the applications of the brake could be widened from those applied only to electric motors.